1. Field of the Invention
The present invention relates to a mobile communication system and a mobile communication method, more particularly to a technology which enables communication of a mobile station within a communication area (CELL) even if a wireless base station runs short of communication resources.
2. Description of the Related Art
If a number of users of portable telephones simultaneously start their communications within a small area, a wireless base station of the area may temporarily run short of communication resources. For example, in an occasion when a number of people gather in a narrow area, such as a music concert or the like, if a number of portable telephones simultaneously demand for calls, the calls cannot be made temporarily. In order to deal with such a shortage of communication resources of the wireless base station, a W-CDMA system has recently started to be adopted in a mobile communication system. However, it is not practical to change a method of the mobile communication system in order to deal with a temporary shortage of communication resources of the wireless base station in a special case as described above.
There has been disclosed a technology capable of dealing with the above-described shortage of communication resources of the wireless base station. Japanese Patent Laid-Open No. 2000-82989 discloses a mobile station capable of operating in a base station mode. This mobile station can dynamically construct a local area network when there is no base station. In Japanese Patent Laid-Open No. 2001-268636, when a mobile station in a predetermined area receives a control signal, the mobile station stops communication with a base station. As another related technology, in Japanese Patent Laid-Open No. 2003-61136, when a first mobile station cannot access a wireless base station, the first mobile station detects a nearby second mobile station and transmits information thereto. The second mobile station transmits the information to the base station.